ABSTRACT: Detritus is a ubiquitous and diverse component of the pelagic ecosystem. It comprises a wide class of particles created by such diverse processes as cell death, egestion, and aggregation. Detrital particles span several orders of magnitude in size and have distinctly different chemical and physical properties. As a consequence, the propensity of detrital particles to serve as substrates for bacteria or grazers, passive particles drifting through the ocean, or conduits for rapid flux into the deep ocean is highly variable. In this chapter, we review the diverse nature of detrital particles and corresponding production and loss terms in the pelagic ocean, as well as current attempts to include detritus in ecological and biogeochemical models. Our goal is to bridge the gap between field experiments and modeling studies by highlighting properties of detritus that vary predictably between classes and can be both measured in the field and incorporated into the next generation of pelagic ecosystem models.